1. Field of the invention
The present invention pertains to a compound transistor circuitry consisting of a combination of bipolar transistors, and more particularly to a compound transistor circuitry of bipolar transistors which requires no or neglible amount of input offset current for operation.
2. Description of the prior art
There has been desired a transistor having a high input impedance as well as a high gain, to make it possible to easily materialize an amplifier circuit of a simple arrangement which provides a high gain and a high input impedance. The existing transistors such as a bipolar transistor and a field effect transistor, however, cannot fully meet these requirements.
A bipolar transistor has a drawback that its input impedance is fairly low since it requires a considerable amount of input offset current for operation. In contrast thereto, a field effect transistor is superior to a bipolar transistor with respect to the input impedance requirement, but on the other hand, its possible gain is, in general, pretty poor as compared with a bipolar transistor.